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Anesthesia Concepts > Scavenging/Capnography/CO2 - EXAM 2 > Flashcards

Scavenging/Capnography/CO2 - EXAM 2 Flashcards

0
Q

recommended max level of volatile anesthetic alone

A

2 ppm

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1
Q

Definition of Scavenging

A

COLLECTION of excess gases from equipment used in administering the anesthesia exhaled by the patient

REMOVAL of these excess gases to an appropriate place of discharge outside of the working environment

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2
Q

recommended level of NO

A

25 ppm

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3
Q

recommended level of VA + NO

A

0.5 ppm

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4
Q

5 basic components of a scavenging system

A 
gas collecting assembly
transfer means
scavenging interface
gas disposal tubing 
gas disposal assembly
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5
Q

what are the widths of the transfer means tubing?

A

19 mm or 30 mm

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6
Q

Within the gas collecting assembly, what happens when the patient expires and it goes into the reservoir bag…?

A

the APL will pop off to allow excess pressure or volume out into the scavenge

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7
Q

Within the gas collecting assembly, what happens if the patient exhales through the vent?

A

the ventilator relief valve will pop off for the gas to move into the scavenging system

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8
Q

at what point is a little bit of volume removed from the circuit?

A

at the gas analyzers or capnography part

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9
Q

what happens to the volume of gas removed from the circuit?

A

it also goes into the scavenging system

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10
Q

what does the gas collecting assembly do?

A

captures gas at the site of emission

delivers gasses to the transfer means

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11
Q

what does the transfer means do?

A

conveys gas from the collecting assembly to the interface

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12
Q

Describe the structure of tubing in the transfer means

A

short and wide to accommodate large volumes without a significant increase in pressure

has female-fitting connectors on both ends

must be kink resistant with stiffer tubing

colored yellow

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13
Q

what is the function of the scavenging interface?

A

prevents pressure increases or decreases in the scavenging system from being transmitted into the breathing system

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14
Q

How could negative or positive pressure be created in the scavenging system?

A

positive - created by PPV

negative - created by the vacuum

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15
Q

what is the range of pressure that the interface will allow?

A

0.5 - 5 cmH2O

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16
Q

describe the structure of the interface tubing

A

30 mm male connecter

should be situated very close to the gas collecting assembly

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17
Q

what are the 3 basic elements of the interface?

A

positive pressure relief - protects patient in the event of an occlusion
negative pressure relief - limits subatmospheric pressure
reservoir capacity - matches the gas flow of the collecting assembly to the continuous flow of the disposal system

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18
Q

what are the 2 types of interfaces?

A

open or closed

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19
Q

open type interface

A

hard rigid casing with holes at the top
any excess volume that comes in will blow out the holes
the holes can be connected to a vacuum system to evacuate the gas

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20
Q

what are the benefits of the open interface system?

A

only uses a vacuum and the environment
there are no valves to control
you can’t generate any excess positive or negative pressure

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21
Q

what sort of adjustments can you make in the closed type interface?

A

there are separate valves for positive and negative relief and you can dial them up or down for how much pressure you want to let out of the system

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22
Q

In the open type interface, what factor is important to consider when you’re deciding on the suction level of the vacuum?

A

the rate should be higher than the rate of FGF so as to not create OR pollution

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23
Q

how does the positive pressure relief valve work on the closed type interface?

A

passive disposal – no vacuum used and no reservoir bag needed

it will open when a max pressure is reached

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24
Q

How does the negative pressure relief valve work in conjunction with the PPRV in the closed type interface?

A
  • uses a reservoir bag
  • has an active disposal system with a vacuum control valve to prevent reservoir bag from overinflation or complete collapse
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25
Q

what is the “backup” for the NPRV and PPRV used in a closed system?

A

a back up negative pressure relief valve will open at -1.8cmH2O if the primary mechanisms have failed for some reason

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26
Q

describe the structure of the gas disposal tubing

A

should be a different COLOR AND SIZE than the breathing system
should be short and wide
usually run overhead to prevent kinking or obstruction

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27
Q

Where is the gas disposal tubing located?

A

between the interface and the disposal assembly

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28
Q

what are the 2 types of a gas disposal assembly?

A

active - gasses move because of mechanical flow which creates negative pressure in the tubing and requires a NPRV

passive - pressure in the system exceeds atmospheric pressure when the patient exhales or the reservoir bag is squeezed (requires positive pressure)

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29
Q

What are the advantages and disadvantages of a passive type disposal system?

A

Advantages - simple to set up, inexpensive

Disadvantages - may be impractical in some buildings

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30
Q

How are waste gases removed in a passive system?

A

through an open window or a fan to the outside air

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31
Q

what are the advantages and disadvantages of an active type disposal system?

A

advantages - convenient in large hospitals with multiple machines running

disadvantages - major expense to set up this system, needle valves need continuous adjustment

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32
Q

How is gas removed in an active type disposal system?

A

the exhaust is connected to a hospital vacuum system via an interface that is controlled by a needle valve

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33
Q

how do you do a scavenging system check?

A
  1. ensure proper connection b/w the scavenging system, APL valve, ventilator relief valve
  2. occlude the Y piece and completely open the APL valve
  3. with minimal O2 flow, allow the reservoir bag to collapse completely and make sure that the pressure gauge reads 0
  4. turn on the O2 flush and allow the scavenger bag to fully distend but verify that the pressure gauge read less than 10 cmH20
  5. then turn off the O2 flush and make sure that the gauge doesn’t read less than 0
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34
Q

what is the danger in forgetting to check the scavenging system before a case?

A

there is no alarm system if the system fails during a case

35
Q

Why do we use capnography?

A

confirm ETT placement
to determine if patient has effective ventilation
to detect abnormalities in V/Q ratio

36
Q

What are some of the abnormalities that could potentially be discovered through the use of capnography?

A 
PE - ETCO2 will be low 
MH
disconnect in the system
obstructed airway
hypotension - really low ETCO2 b/c you aren't perfusing
37
Q

under what circumstances would ETCO2 increase?

A

hypoventilation (low RR or low Vt)
obstructive respiratory disease (patient takes longer to exhale CO2)
increased metabolism (MH, stress, sepsis)
decrease in FGF (CO2 scrubber kicked, rebreathing)

38
Q

When would ETCO2 decrease?

A 
hypothermia
hyperventilation
low CO
hypovolemia
leak in the system (false low CO2)
39
Q

How can you determine PaCO2 from ETCO2?

A

Under GA, PaCO2 is generally 2-5 mmHg less than ETCO2

40
Q

what are the 2 methods for assessing the CO2 content of expired gas?

A

colorimetric or infrared absorption spectrophotometry

41
Q

how does colorimetric CO2 measurement work?

A

CO2 combines with H2O on the paper and forms carbonic acid that turns the paper a different color

42
Q

How does infrared absorption spectrophotometry work?

A

when the gas is exhaled the proportion of its components is analyzed and each gas will absorb infrared radiation at different wavelengths

43
Q

mainstream capnography

A

a airway adapter hooked up to a transducer is placed directly on the end of the breathing circuit where the patient exhales

44
Q

what are the disadvantages of using mainstream capnography?

A

potential for burns b/c it generates lots of heat
it can be heavy, causing kinks in the ETT
mucous can block the system from reading correctly

45
Q

What are the advantages of using mainstream capnography?

A

there is less of a time delay

46
Q

how does the sidestream capnography work?

A

takes a fixed volume from the circuit away from the patient and uses IR analysis to compare the CO2 sample with a known quantity

47
Q

What are the advantages of using sidestream capnography?

A

gas it taken away from the patient and less potential for burns

48
Q

what are the disadvantages of using sidestream capnography?

A

there is a slight time delay
potential disconnect source
dilution of the sample in pediatric patients r/t lower Vt
water vapor can condense in the system and filters are required

49
Q

What is Phase 1 of the capnography waveform?

A

inspiratory baseline
no CO2
dead space gas is exhaled

50
Q

What is Phase 2 of the capnography waveform?

A

the expiratory upstroke that represents rising CO2
mixture of alveolar and dead space gas
slope of the upstroke determined by evenness of alveolar emptying

51
Q

At what point does the machine measure the ETCO2?

A

at the end of Phase 3

52
Q

What is Phase 3 of the capnography waveform?

A

the longest phase (called the alveolar plateau)
end expiration
a reflection of PACO2 and PaCO2

53
Q

What is phase 4 of the capnography waveform?

A

beginning of inspiration

CO2 levels rapidly decline to a normal inspired value

54
Q

What are the 5 characteristics of the capnography waveform that are important to consider?

A 
frequency
rhythm
height
baseline
shape
55
Q

presence of stable CO2 for ***** breaths indicates tracheal intubation

A

3

56
Q

What type of changes will be noticed on the capnography waveform for a patient with obstructive disease

A

slow rate of rise in Phase 2

little or no Phase 3

57
Q

What sort of waveform will you have if the ETT has gone into the esophagus?

A

no consistent waveform, progressively decreasing waves

58
Q

How will you know if rebreathing occurs?

A

if your inspiratory baseline continues to remain above 0 at the end of phase 4

59
Q

what are some causes of rebreathing?

A

decrease in FGF, exhausted CO2 scrubber, dead space caused by equipment

60
Q

how can you tell that your patient has started to spontaneously ventilate by using the capnography waveform?

A

there will be a curare cleft, or a small deflection, in the phase 3 portion of the waveform

means that the patient is starting to wake up from their neuromuscular blockade and the diaphragm is moving

61
Q

what is the problem with noting cardiac oscillations?

A

NOTHING - they’re normal

62
Q

what are some of the causes of rising CO2 is ventilation-related factors have been excluded?

A

Malignant hyperthermia
tourniquet release (releases lactic acid and metabolic byproducts)
release of aortic clamp
IV bicarb administration
CO2 blowing into peritoneal cavity
equipment failure (CO2 exhausted, expiratory valve stuck)

63
Q

What are some causes of a decreasing CO2 tracing?

A

hyper ventilation
cardiac arrest
disconnect within the system
V/Q mismatch (r/t PE??)

64
Q

What compound is the CO2 scrubber actually sensing?

A

H2CO3 - carbonic acid

65
Q

what is the pattern of absorption in the CO2 scrubber?

A

from top to bottom

66
Q

What are some of the more common types of absorbent?

A

Amsorb Plus
Soda Lime
Litholyme

67
Q

Litholyme

A

made of lithium hydroxide

68
Q

Soda lime composition

A

80% CaOH2
15% H2O
4% NaOH
trace silica and KOH

69
Q

Why is water added to the CO2 scrubber system?

A

to facilitate the reaction to CO2 to form the carbonic acid

70
Q

why is silica added to soda lime?

A

to increase hardness and prevent dust from forming

71
Q

What is the average absorptive capacity of a soda lime scrubber?

A

26L/100g

72
Q

On average, how much CO2 is released by a non-stressed person each hour?

A

12L CO2

73
Q

What are the chemical reactions as CO2 moves through a soda lime scrubber?

A

CO2 + H2O = H2CO3
H2CO3 + 2NaOH = Na2CO3 + 2H2O + heat
Na2CO3 + CaOH2 = CaCO3 + 2NaOH

*can also use KOH;K2CO3

74
Q

Composition of Amsorb

A

80% calcium hydroxide
16% H2O
1-4% calcium chloride
trace calcium sulfate for hardness

75
Q

absorptive capacity of amsorb

A

10L/100g

76
Q

What chemical reactions take place when CO2 enters an amsorb scrubber?

A

CO2 + H2O = H2CO3

H2CO3 + CaOH2 = CaCO3 + 2H2O + heat

77
Q

When should you replace your CO2 absorber?

A

when its at 50-70% color change

78
Q

what is the ideal shape of the absorbent crystals? why?

A

4-8 mesh

to create ideal surface area without increasing resistance

79
Q

what should the hardness number be for the granules?

A

> 75

80
Q

what is “channeling”?

A

preferential passage of gas through the absorber via pathways of least resistance

results from loosely packed crystals

81
Q

How can you prevent channeling?

A

shaking the canister around a little bit before you use it

82
Q

dry soda lime may degrade inhaled anesthetics to ****

A

Carbon monoxide

83
Q

What is the danger with leaving an oxygen source on over night, running through the scrubber?

A

carbon monoxide will build up in the system and could cause poisoning

84
Q

How can you prevent degradation of the VA/scrubber?

A

run your flows at a rate of at least 2L/min

85
Q

what can sevoflurane/halothane degrade to when it passes through soda lime?

A

Compound A = nephrotoxic

86
Q

What are some safety considerations when using a CO2 scrubber?

A

change it every morning
turn off gas flows when not in use
change all absorbent, not just one canister
keep flows low to preserve humidity

Anesthesia Concepts (8 decks)

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